Contact-free thickness measurements play an increasingly important role in industrial process monitoring and quality control. In automotive manufacturing, the exact thickness of paint and coating layers plays a crucial role not only for the overall appearance, but also for protection against UV radiation and corrosion. In pharmaceuticals, the coating thickness governs the release of the drug inside the body, with consequences on the efficacy and potential side effects. In chip production, highly homogeneous polymer coatings act both as protection against moisture and dust and as stress absorbers.

Most of the traditional thickness gauges require physical contact to the layer under test, and fail in case of non-metallic substrates. Terahertz pulses, by contrast, resolve the thickness of each individual layer, as long as adjacent coatings differ in their refractive index. Non-contact measurements in transmission or reflection geometry can even monitor drying or curing processes of wet coatings. The analysis combines time-of-flight measurements of terahertz pulse echoes with elaborate data post-processing, which involves Fourier transformations and advanced fitting routines. This method has proven successful: TOPTICA’s customers have achieved thickness measurements down to 20 µm, with accuracies on the single-micron level.